Illumination device and method for decoupling power delivered to an LED load from a phase-cut dimming angle

ABSTRACT

An illumination device and method are provided for controlling light-emitting diodes (LEDs). The LEDs (specifically, the LED loads) are controlled, e.g., brightness and color of the LED loads, independent of a phase-cut dimmer applied to the AC mains feeding a DC power supply. The power supply is active dependent upon the duration of a conduction angle supplied from the dimmer. The power supply, however, produces drive currents that are independent from the conduction angle by using a two-stage power supply and a relatively slow and fast control loops that are controlled through a microprocessor-based control circuit. Parameters stored in the control circuit are drawn by the microprocessor to control the two-stage power supply to produce the drive currents independent and decoupled from the conduction angle yet dependent on the controller parameters.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/014,790, filed Feb. 3, 2016, the entirety of which is incorporatedherein by reference, which is related to application Ser. No.15/014,899, filed Feb. 3, 2016, titled “Illumination Device and Methodfor Independently Controlling Power Delivered to a Load from DimmersHaving Dissimilar Phase-Cut Dimming Angles”, now U.S. Pat. No.9,655,188, and to application Ser. No. 15/014,925, filed Feb. 3, 2016,titled “Device and Method for Removing Transient and Drift from an ACMain Supplied to a DC-Controlled LED Load”, now U.S. Pat. No. 9,655,178.

BACKGROUND OF THE INVENTION 1. Field of the Invention

This invention relates to illumination devices comprising light emittingdiodes (LEDs) and, more particularly, to LED illumination devices thatuse phase-cut dimmers.

2. Description of the Relevant Art

The following descriptions and examples are provided as background onlyand are intended to reveal information that is believed to be ofpossible relevance to the present invention. No admission is necessarilyintended, or should be construed, that any of the following informationconstitutes prior art impacting the patentable character of the subjectmatter claimed herein.

Lamps and displays using LEDs for illumination are becoming increasinglypopular in many different markets. LEDs provide a number of advantagesover traditional light sources, such as incandescent and fluorescentlight bulbs, including low power consumption, long lifetime, nohazardous materials, and additional specific advantages for differentapplications. Mainstream usage of LED illumination devices has steadilyincreased over the years with advancements in LED technology and theresulting decreasing costs.

Many lighting applications use light dimmers to adjust the powerdelivered to the light sources, and therefore, control the intensity oflight generated by the light source. Commercially available dimmers comein many different varieties with many different characteristics. Somedimmers comprise micro controllers, which typically are calledelectronic dimmers, while others comprise only passive components.

The vast majority of dimmers used in residential or commercialapplications are phase-control devices (otherwise referred to asphase-cut dimmers), which were initially designed as a simple,efficient, and inexpensive method to dim incandescent light sources.Phase-cut dimmers, both leading-edge and trailing-edge, generallyoperate by limiting the power delivered to the load by conducting only acertain percentage of the AC waveform each half-cycle. In leading-edgephase-cut dimmers, the forward phase, or leading edge, of the ACwaveform is removed from each half-cycle to limit the power delivered tothe load. Conversely, trailing-edge phase-cut dimmers limit the powerdelivered to the load by removing the reverse phase, or the trailingedge, of each half-cycle. In both cases, slight dimming is achieved byremoving a relatively small portion of the AC waveform, whereas a largerportion is cut for deeper dimming. Manually varying the dimmer positionvaries the conduction angle and the conduction period, and hence, thepower delivered to the load, resulting in a change in light output. Mostphase-cut dimmers are wall-mounted devices powered by an AC mains linevoltage of 120V RMS at 60 Hz or 220V RMS at 50 Hz.

FIG. 1 illustrates an example of a typical dimmer-controlledillumination device. Dimmer 10 is coupled to the AC mains line andproduces a corresponding conduction angle at its output. An example of arectified leading-edge conduction angle 12 is shown applied to aconventional power supply 14. If illumination device 16 is used toilluminate an LED load made up of one or more LED chains 18, then thepower supply 14 typically includes an AC/DC converter that converts thephase-cut AC waveform at a manually adjustable conduction angle to a DCvoltage (V_(DC)). From the DC voltage, current of varying magnitude canbe applied to the LED load 18 depending upon the brightness needed aswell as the color spectrum desired if more than one red, green, blue, orwhite LED chain is used. Driver 20 can be used to drive the differentLED chains to produce the desired brightness in lumens, and thedifferent desired color spectrum.

FIG. 2 illustrates the conduction angle 12 of a leading-edge phase-cutdimmer. It is well known that the conduction angle can be a trailingedge as well, and that conduction angle 12 is simply an example of onetype of conduction angle formed by a phase-cut dimmer. The cross-hatchportion of the AC main waveform indicates the remaining phase-cut ACmains signal.

When used with an LED load, commercially available phase-cut dimmersprovide inconsistent performance when dimming LEDs. One reason is in thedesign of an LED load versus an incandescent load. For example, anincandescent illumination device presents a simple resistive load with alinear response. Phase-cut dimmers work particularly well with this typeof load, since the resistance of the filament decreases as itsconduction angle decreases, resulting in naturally smooth dimming.

On the other hand, LED loads do not present a simple resistive load tothe dimmer. Instead, most LED loads can be characterized by adiode-capacitor power supply feeding a constant current source. Thediodes rectify the applied AC voltage allowing it to charge the storagecapacitor, while the LED loads draw a constant current from the powersupply that is related to the desired dimming level and brightness. Inthe diode-capacitor power supply model of the LED load, current flowsfrom the applied voltage to the load only when the magnitude of theapplied voltage exceeds the stored voltage on the power supplycapacitor, often coupled to the output of the power supply. The storedvoltage on the power supply capacitor, in turn, depends on the currentdrawn by the LEDs themselves, which is a function of the LED brightness.Therefore, the current flowing from the power supply to the LED dependsboth on the instantaneous value of the AC voltage waveform and thebrightness of the LED, which is dependent upon the dimmer conductionangle.

In conventional dimmer design, the current flowing to the LED load isrelated or relative to the conduction angle output from the dimmer. Forexample, in a single stage switched mode power supply, the energystorage element, either inductor or capacitor, must supply power to theLED while the triac dimmer, for example, is not conducting. As theconduction angle changes, the energy stored in the energy storageelement (e.g., the diode-coupled capacitor or current-storage inductorat the output of the power supply), must therefore provide power forchanging amounts of time. For example, as the conduction angledecreases, the energy storage element must provide power for increasingamounts of time. To keep the ripple current through the LED loadrelatively constant, the LED drive current through the LED load mustdecrease with decreasing conduction angle. The reverse is true if theconduction angle increases.

FIG. 5 illustrates the relationship between the dimmer conduction angleand the brightness of, for example, an incandescent load. Many dimmershave varying ranges of conduction angle that they can produce. Someproduce conduction angles between 60° and 120°, while others can producea wider range of conduction angles. As the dimmer is manually adjusted,either by rotating a knob or moving up and down a slider on a wallplate, the load responds accordingly; typically, in linear fashion asshown. In the example of FIG. 5 , the angle range from some dimmers mayextend from 90° indicating maximum brightness to 45° indicating minimumbrightness, while the angle range of other dimmers may extend from 165°downward to 15°; additionally, the angle range of some dimmers canchange between the first time such dimmers are turned on and subsequentoperation of those dimmers. For instance, some dimmers may first turn onwith a minimum angle of 45°, but once on, will produce angles down to30°.

As noted in conventional dimmer design, power supplied to the load,whether LED or not, is dependent on the conduction angle. If morebrightness is needed, the conduction angle must be increased therebyincreasing the power drawn from the AC main line and thus the loadcurrent supplied to the load. A power supply that produces the drivecurrent to the LED load is therefore dependent on, and coupled to, theconduction angle output from the dimmer. It would be desirable todecouple the power supply from the conduction angle in certain instanceswhere an LED load is used. For example, when different dimmers are used,it may be desirable to detect the differing conduction angle ranges ofthe newly attached dimmer and adjust the mapping of the conduction angleto the brightness required by the LED load. In this way, the LEDs canadapt to whatever attached dimmer is used, so that the full mechanicalrange of a sliding or rotating dimmer can be employed to adjust to anydesired LED brightness. Additionally, the LEDs and, more specifically,the LED drive currents applied thereto, can dynamically change therelationship between the input conduction angle and the brightness whenattached to dimmers that have a different angle range when first turnedon. As such, the LEDs will not “pop on” when such a dimmer is firstincreased from a minimum conduction angle setting.

Moreover, conventional LED illumination devices deliver power to the LEDload proportional to the RMS voltage of the AC main, where the AC maincan vary both in angle and amplitude. For example, those AC mainvoltages can vary by +/−20% or more from a nominal value causing thebrightness of the LEDs to vary accordingly. Additionally, the minimumbrightness is determined by the RMS voltage at the minimum angle fromthe dimmer. The minimum RMS voltage can be substantial, which thenresults in the minimum light output from the LEDs being quite bright,and barely less than a few percentages of the maximum brightness.

Most residential or commercial LED lighting applications come equippedwith dimmers, and preferably triac dimmers. However, as noted above,coupling the unique characteristics of drive currents to LEDs and theattempted control of same using a dimmer coupled to the AC main line isproblematic. While it is beneficial to retain the dimmer since mostresidential and commercial applications include a dimmer, it is alsobeneficial to remove LED output control from being controlled by thedimmer. Thus, decoupling the dimmer conduction angle output from LEDoutput is beneficial not only to enhance the range of LED output fromthat available using a dimmer but also to accommodate dimmers havingdiffering conduction angles yet maintaining a more precise LED outputcontrol than that available using conventional dimmer designs. Most ofall, it is of benefit to decouple the conduction angle from the powersupply, which conventional dimmer-controlled illumination devices cannotachieve. However, if decoupling were to occur beyond what is currentlyavailable in conventional dimmer designs, the power supply would be ableto control the minimum light output to be independent of the minimumconduction angle and to be arbitrarily small, for example, 0.1% of themaximum brightness of the LED output. This is much lower than what canbe achieved using conventional dimmer-controlled illumination devices.Likewise, conventional dimmers that produce a relatively small maximumangle, for example, 90°, have correspondingly smaller maximum outputbrightness than those dimmers having a maximum angle greater than 90°.Decoupling the power supplied to the LED load from the conduction anglewould enable the maximum brightness to be independent of the maximumconduction angle obtainable by the dimmer. This benefit not being onethat a conventional dimmer-controller illumination device can achieve.

Although the RMS line voltage can vary with angle and amplitude, certaintransients and drift can also be present from the output of aconventional dimmer-controlled illumination device. As shown in FIG. 3 ,the output of a leading edge phase-cut dimmer 10 (FIG. 1 ) can havecertain transients 22 that occur when the line voltage is rectifiedinitially to a relatively large voltage value with oscillationsoccurring on the leading edge of the conduction angle. In addition, atthe conclusion of each conduction angle, leakage current through a triacfor instance can cause the AC main line voltage into the lamp to drift,which can adversely affect the next conduction angle measurement. Asshown, between conduction angles when a triac is supposedly off and thepower supply is also off, small leakage currents may still flow throughthe triac. Leakage current causes upward DC drift 24 between conductionangles and, importantly, at the critical time in which the conductionangle is being measured by the power supply. If the triac resets priorto the AC mains rectified voltage dropping to near zero volts, the powersupply might measure an incorrect conduction angle or may prevent thepower supply from working properly. The combination of AC transients 22and DC drift 24 can deleteriously affect measurements taken at powersupply 14 coupled to receive the rectified AC main; thus, furtheraffecting the brightness control on the LED load 18. As shown in FIG. 4, changes in conduction angle 26 can cause skew so that thecorresponding brightness is not robust throughout the entire conductionangle range. In addition, transients and drift can affect the robustnessof the brightness being controlled by the power supply.

In order to deliver smooth brightness control over a much wider rangeand to adapt to any conduction angle range of any attached dimmer, itwould be desirable to introduce an improved power supply architecture.The improved power supply must be one that can decouple power deliveredto the LED load from the conduction angle so that the power deliveredderives from a source other than the dimmer and, thus, is independentfrom the conduction angle. The improved power supply can then adapt apower output to the LED load for any dimmer or conduction angle range ofa dimmer applied to an AC mains line, and can operate at brightnesslevels much lower than conventional power supplies so as to dim a lampto less than 0.1% of the maximum brightness of that lamp, for example.It is further desirable for the improved power supply to remove the ACtransients and DC drift so as to achieve a more precise reading of theconduction angle, and also to know more precisely when to activate thepower supply, and modify the DC power supply current at each conductionangle duration for more precise control of the drive current across abroader range of LED brightness.

SUMMARY OF THE INVENTION

The problems outlined above are in large part solved by systems andmethods for luminance control of illumination devices by decouplingpower delivered to an LED load from the phase-cut dimming angle. Thosedevices and methods also have the ability to independently control powerdelivered to a load from dimmers having dissimilar phase-cut dimmingangles. Any transient and drift from an AC main supplied to aDC-controlled LED load are effectively removed using the improvedillumination devices and methods described herein below.

According to a first embodiment, an illumination device is providedhaving an AC main line configured to receive an AC mains. An LED load iscoupled to receive a drive current, and a dimmer is coupled to the ACmain line. The power delivered to the LED load is decoupled from theconduction angle in that the LED drive current is not set by the dimmer,or the conduction angle output from the dimmer. Instead, the LED drivecurrent is controlled in part by a microcontroller-based controlcircuit. Control circuit parameters can be set within a memory of themicrocontroller, either directly or through radio commands. Thoseparameters can then be used by, for example, comparators in a DC powersupply coupled between the dimmer and the control circuit.

Changes in LED drive current needed to achieve a desired brightness orcolor mix of the LED output are controlled by the control circuit. Thosechanges affect a DC voltage (V_(DC)) output from the power supply. Thepower supply provides V_(DC) to, for example, a diode-coupled outputcapacitor from which current is drawn as drive currents to the LED load.V_(DC) is regulated by the power supply. For example, more power isdrawn from the AC main line when V_(DC) starts to drop and less power isdrawn when V_(DC) starts to rise.

The power supply includes a main, or first, control loop (slow loop) anda second control loop (fast loop). The first control loop is a secondorder loop with an output integrating capacitor on V_(DC) and a loopstabilizing proportional-integral (PI) filter. The output of the loopfilter represents the average current drawn from the AC main linemeasured over more than one cycle of the AC main (I_(AVE)). Since the ACmains line voltage is varying and is phase cut by the dimmer, the powersupply converts I_(AVE) to the time during each conduction angle inwhich the DC power supply is active (T_(PON)) and the DC power supplycurrent that is drawn from the line during this time (I_(PS)). A highbandwidth first order loop within the main control loop (i.e., secondcontrol loop) ensures that the actual power supply current (I_(ACT)) isroughly equal to I_(PS) during T_(PON). A control circuit can be coupledto receive transitions of the AC main and to measure a conduction anglefrom the dimmer. The control circuit can produce a maximum duration atwhich the power supply can be active so that the power supply coupledbetween the dimmer and control circuit is operational up to andincluding a maximum duration as measured by the control circuit. Thepower supply is further configured to receive the LED drive currentindirectly through variations in V_(DC) and apply an updated DC powersupply current, independent of the conduction angle yet for a durationno greater than the maximum power supply active duration.

The power supply according to one embodiment is coupled to the output ofthe dimmer and comprises a first control loop for producing a DC powersupply voltage output (V_(DC)) and therefore the LED drive current fromthe DC power supply voltage output, independent of the conduction angle.The power supply state machine is triggered from periodic transitions ofthe AC main line and is active only while there is sufficient AC mainsvoltage to deliver power to V_(DC). The output capacitor on DC powersupply V_(DC) stores energy that is delivered continuously to the LEDload when the power supply is not active. The LED load is coupled toreceive the DC power supply maintained on the output capacitor forsufficient duration to produce illumination for the illumination device.

In addition to the first control loop of the power supply configured toproduce the DC power supply and DC power supply duration, the powersupply also comprises the second control loop having a higher bandwidththan the first control loop. The second control loop is configured toproduce a series of pulses, and the duration of the cumulative series ofpulses corresponds to the DC power supply duration, and the duration ofeach of the series of pulses corresponds to the drive current applied tothe LED load.

A method is also provided for supplying an AC main to an LED load,comprising adjusting a dimmer coupled to the AC main and rectifying theoutput of the dimmer. A conduction angle is then measured by measuringthe amount of time between when the AC main is initially rectifiedpositive to when the rectified positive AC main phase angle equals 180°or 360° phase angle. Next, a series of pulses (T_(GATE)) are generatedduring a duration of the conduction angle, each having an active logicvalue dependent on the amount of drive current supplied to the LED load.The active logic value is independent from the conduction angle and,specifically, the dimmer output.

According to yet another embodiment, the control circuit is contemplatedas one configured to measure a range of conduction values whenever thedimmer circuit produces such a range, extending from when the dimmer isfully off to when the dimmer is fully on. The control circuit measuresthe range of conduction angles and can produce a maximum duration atwhich the power supply can be active based on the conduction anglesmeasured. Thus, for example, if a conduction angle output from thedimmer is at 90°, the control circuit measures that conduction angle andsets the maximum time in which the power supply is on. Using thatmaximum duration of the power supply, the power supply is activated upto and including that maximum duration. The drive current produced fromthe power supply ranges upward to the maximum duration but isindependent from the range of conduction angles. As an example, if themaximum duration of the power supply is set to a 90° conduction angle,the power supply can be activated for any amount of time T_(PON) up toand including that max time (Max T_(PON)). Moreover, the current drawnfrom the AC mains line (I_(PS)) can be adjusted to any value during thattime to adjust the DC power supply current averaged over multiple cyclesof the AC main (I_(AVE)) as drawn from the AC main line and which isproportional to the drive current delivered to the LED load and,consequently, proportional to the brightness.

As another example, if the dimmer is set so that it is fully on, themaximum duration produced from the control circuit may be commensuratewith the fully on conduction angle. However, the current produced by thepower supply is independent from that conduction angle yet scaleddownward from a maximum brightness to a minimum brightness. Suchbrightness levels are not set by the dimmer, but by the controller whichcontrols the DC power supply current as well as the duration at whichthe power supply is on. Such controller is not operated through changesof the manually controlled dimmer, but through parameters stored in thecontroller, and specifically within memory of the microprocessor-basedcontroller. The parameters can be stored in firmware or periodicallyupdated through read/write memory via a radio using wireless control,for example. The wireless control can be derived using a wirelesscommunication channel protocol, such as IEEE 802.11 or 802.15. A popularwireless control communication protocol is ZigBee, for example.

Accordingly, a method is provided for supplying an AC mains to an LEDload by adjusting a dimmer coupled to the AC main between a minimumconduction angle and a maximum conduction angle. Alternatively, thedimmer can simply be set to any conduction angle and utilizing thatconduction angle as a maximum conduction angle from which brightness canbe controlled. The amount of DC power supply current drawn from the ACmains can then be determined by the power supply loop by monitoring theDC power supply output voltage supplied as drive current to the LEDload. Furthermore, the amount of DC power supply current drawn from theAC main can be changed independent from what the dimmer indicatesthrough conduction angle. In this case, the maximum power drawn from theAC mains line is typically determined by the maximum peak currents thatthe power supply internal components can tolerate.

According to yet another embodiment, the illumination device comprises adamping circuit coupled to the AC main line. The power supply is coupledbetween the dimmer and the controller to activate the damping circuit. Arelatively slow timing circuit is coupled to the power supply and isoperated at a clock speed no more than the regular periodic intervals ofthe AC main. The timing circuit is configured to activate the dampingcircuit during the duration of the intervals between the conductionangles and also during the initial portion of the duration of theconduction angles to remove transients from the AC main line. Thosetransients existing primarily at the initial ramp up of the phase-cutdimming angle or conduction angle.

According to yet another embodiment, the power supply is further coupledto activate a bleeding circuit also coupled to the AC main line. Therelatively slow timing circuit is further configured to activate thebleeding circuit during the final portion of the conduction angle duringthe cycles when phase angle is being measured to maintain sufficienttriac holding current, which prevents the triac from resetting beforethe end of the conduction angle. The bleed circuit and the power supplyare activated when the triac is ideally not conducting to remove anyvoltage from the AC main line at the beginning of conduction anglemeasurements. The bleeding circuit preferably comprises a current sourcethat draws a fixed current from the AC main line so as to maintain thedimmer in an “on” state and to prevent it from latching into an “off” orinactive state, such as what might occur if there is insufficientcurrent through a triac-type dimmer.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become apparent uponreading the following detailed description and upon reference to theaccompanying drawings.

FIG. 1 is one example of a block diagram of a conventionaldimmer-controlled, LED-based illumination device;

FIG. 2 is a timing diagram of the AC main applied to, for example, atrailing-edge dimmer;

FIG. 3 is a timing diagram of the conduction angle from the leading-edgedimmer having transients at the leading edge of the conduction angle anddrift between conduction angles;

FIG. 4 is a timing diagram showing the variability of a 90-degreeconduction angle as a result in changes made to, for example, atrailing-edge dimmer;

FIG. 5 is a graph of conduction angle vs. brightness that is relativelylinear but with variable ranges of conduction angle and brightness;

FIG. 6 is a block diagram of a dual stage power supply that controls anLED load decoupled and independent from a conduction angle produced bythe dimmer;

FIG. 7 is a block diagram of the power supply having fast and slowcontrol loops for measuring duration of the conduction angle by the slowcontrol loop and actual instantaneous current drawn from AC main by thefast control loop to set the DC power supply current drawn from the ACmain and supplied to the LED load during each conduction cycle;

FIG. 8 is a state diagram of the I_(AVE) mapping sequential circuit ofFIG. 7 ;

FIG. 9 is a state diagram of the I_(ACT) calculation circuit of FIG. 7 ;

FIG. 10 is a timing diagram of the I_(ACT) computation point taken fromI_(PK) value, and T_(GATE) and T_(G2I) timing values;

FIG. 11 is a circuit diagram of the AC/DC analog block diagram of FIG. 7;

FIG. 12 is a timing diagram showing signals sent to and from the fasttiming circuit of FIG. 7 ;

FIG. 13 is a timing diagram showing signals sent to and from the slowtiming circuit of FIG. 7 for when the power supply draws greater powerfrom the AC main line and produces a corresponding greater current ontothe LED load;

FIG. 14 is a timing diagram showing signals sent to and from the slowtiming circuit of FIG. 7 for when the power supply draws smaller powerfrom the AC main line and produces a corresponding smaller current ontothe LED load; and

FIG. 15 is a block diagram of the control circuit and processor withinthe control circuit for measuring conduction angle and the maximum timein which the power supply is on.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and will herein be described in detail. Itshould be understood, however, that the drawings and detaileddescription thereto are not intended to limit the invention to theparticular form disclosed, but on the contrary, the intention is tocover all modifications, equivalents and alternatives falling within thespirit and scope of the present invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An illumination device and method are disclosed for luminance control ofan LED load. Specifically, the illumination device includes a dimmercoupled to an AC main line and a power supply coupled between the dimmerand the LED load. Coupled to the power supply is a control circuithaving a microprocessor. The control circuit measures the conductionangle output from the dimmer onto the input of the power supply. Fromthat conduction angle, the control circuit can determine the maximumtime duration at which the power supply can be active. The active powersupply produces a drive current onto the LED load independent of theconduction angle, albeit relative to the maximum time it is active.Instead of being dependent on the conduction angle as in conventionalpower supplies, the improved power supply herein comprises two stages,wherein the first and second stages produce the drive current dependentupon the amount of brightness and color spectrum needed by the LED load,independent of the dimmer angle or conduction angle. The drive currentis controlled by the controller and, specifically, by parameters storedand thereafter fetched from a memory of the microprocessor and thereforeset within the control circuit. The drive current is not set by theconduction angle output from the dimmer, as would be the case inconventional designs. The controller parameters can be set in firmwareduring manufacture or can be periodically reset from a wired or wirelesscommunication device coupled to the controller via the wired or wirelesscommunication channel.

FIG. 6 illustrates one example of the improved illumination device.Specifically, FIG. 6 illustrates a dimmer 30 coupled to an AC main line,such as the well-known AC main lines used in residential or commercialapplications and carrying, for example, a 120V RMS at 60 Hz or 220V RMSat 50 Hz. Dimmer 30 comprises any dimmer that can couple to an AC mainssupply voltage to employ angle modulation of a switching device, such astriac. Such dimmers are relatively well known and are used to adjust theduty cycle of the AC dimmer output signal to provide either aleading-edge phase-cut dimmer output or a trailing-edge phase-cut dimmeroutput. Dimmer 30, whether leading- or trailing-edge, is manuallycontrolled either through sliding or rotating actuators associated witha faceplate mounted in the residential or commercial structure.

Coupled to the output of dimmer 30 can be electromagnetic interference(EMI) circuit 32 to block any disturbance generated by an externalsource onto the AC main line and can include any of the well-knownnarrowband or broadband EMI filtering circuitry. Coupled to the outputof EMI 32 is bridge circuit 34. Common examples of a bridge circuitinclude, for example, a diode bridge. Bridge 34 operates in conjunctionwith dimmer 30 to produce a rectified output (V_(HV)) from the phase-cutAC mains. As noted above, however, V_(HV) has transients at the leadingedge, for example, of a leading edge rectified dimmer output. Moreover,due to the nature of the triac circuitry of dimmer 30, certain triacsmay fail to turn on reliably with reactive loads if the current phaseshift within the triac causes the main circuit currents to be below theholding current at the time in which the triac triggers. Thus, a triaccan “reset” if the current through the triac drops below the holdingcurrent. The problems in conventional design of AC transients on theleading edge of the conduction angle and shift due to improper triacreset are overcome using the architecture set forth in power supplycircuitry 36.

Power supply 36 comprises first stage 38 and second stage 40. Firststage 38 is an AC/DC converter that produces a DC voltage (V_(DC)) fromthe AC main voltage (V_(HV)). Second stage 40 is a DC/DC converter thatproduces the drive current to the LED load 42. Thus, while V_(HV) is afiltered and rectified version of the AC mains voltage produced bydimmer 30, V_(DC) is the DC-converted voltage from V_(HV). V_(DC) feedsa relatively large output capacitor to provide the necessary drivecurrent to achieve the desired brightness and color spectrum whenmultiple LED chains 44 are used. While FIG. 6 illustrates one LED chain,it is understood that power supply 36 can be replicated to produce drivecurrents to other LED chains having a different color spectrum, such asgreen, blue, red, or white, to achieve any desired brightness for eachLED chain and, thus, the proper color mixing across the plurality ofchains.

Differential amplifier 46 is coupled to the AC main line and produces avoltage (V_(IN)) proportional to the AC line voltage V_(HV) sent topower supply 36. V_(IN) is at a sufficiently low voltage value so thatit can be digitized by first stage 38, and thereafter used by thephase-locked loop (PLL) (FIG. 15 ) of control circuit 48. Referring toFIGS. 6 and 15 , control circuit 48 can include a processor 50 alongwith PLL 52 containing a memory and a microprocessor that setsparameters used by the power supply 36 to change the drive current. Thepower supply changes the drive current through the LEDs by use of afirst control loop (slow loop) feedback in response to changes in the DCvoltage output (V_(DC)) from the first stage AC/DC 38. The LED drivecurrent, however, is related and proportional to DC power supply currentaveraged over multiple cycles of the AC main (I_(AVE)) and drawn fromthe AC mains line, whereby any changes to the LED drive current via themicroprocessor-based controller causes average current drawn from the ACmain line (I_(AVE)) to change. The controller also changes the powersupply current drawn from the AC main line during each conduction cycle(I_(PS)) as well as the time that the power supply 36 is on (T_(PON)).Thus, instead of using dimmer 30 to set the drive current, controlcircuit 48 sets the drive current based upon the desired brightnessneeded for each LED chain 44 within LED load 42. Therefore, drivecurrent is set independent from the conduction angle produced by dimmer30, using the present dual-stage power supply 36 controlled by controlcircuit 48. One mechanism in which to set the parameters for controllingthe drive current via control circuit 48 is through a wired or wirelessuser input. An example of a wireless user input includes a wirelesscommunication protocol, such as IEEE 802.15, Bluetooth or ZigBee. Radio54 is shown to interface with the processor of control circuit 48 inorder to set the parameters used to establish any drive currentindependent of the conduction angle output from dimmer 30.

Turning now to FIG. 7 , a block diagram of power supply 36 is shownhaving a fast control loop 58 and a slow control loop 60. In addition,power supply 36 comprises AC/DC analog portion 62, details of which areset forth in FIG. 11 . AC/DC analog 62 receives V_(HV) and V_(IN) fromthe rectified dimmer and differential amplifier (FIG. 6 ). Moreover,AC/DC analog 62 receives certain signals from control circuit 48 (FIGS.6, 15 ). Further details of how the AC/DC analog 62 derives the zerocrossing detect (ZCD) signal and the current comparator (I_(CMP)) signalare described with regard to FIG. 11 . Signals ZCD and I_(CMP) are usedby fast control loop 58, whereas the slow control loop 60 uses a linesense (L_(SNS)) signal derived from V_(IN), details of which are setforth in FIG. 11 . L_(SNS) represents the transitions that occur at theleading and trailing edges of the conduction angle duration computed bythe determination of V_(IN) at the output of differential amplifier 46(FIG. 6 ). In addition to L_(SNS) sent from AC/DC analog 62, a feedbackvoltage (V_(FB)) is sent to slow control loop 60; specifically, to acomparator or adder 64. Comparator 64 compares a divided-down V_(DC)digitized value (V_(FB)) to a target value sent from control circuit 48;specifically, from a stored parameter within processor 50 (FIG. 15 ).The target value (V_(TAR)) is a constant set by the control circuitsoftware such that a divided voltage of V_(DC) that is digitized iscompared to that constant V_(TAR) provided by processor 50 in controlcircuit 48. The difference is applied to integrator 66 which filtersthat difference to produce the DC power supply current averaged overmultiple cycles of the AC main (I_(AVE)) and drawn from the AC mainline. Drive current is that which is applied to the LED load 42. Drivecurrent is proportional to the amount of time that a series of pulsesare applied to the analog portion 62 to affect the DC output voltageV_(DC). Slow control loop 60 is a well-known second order loop with aproportional/integral PI loop filter 66, shown to produce the averagecurrent (I_(AVE)), since the current drawn from the line, I_(AVE), isrepresented as a number output from the proportional/integral loopfilter 66. I_(AVE), when represented as a signal, is proportional to thedrive current produced from the power supply 36, which flows into LEDload 42. The slow loop preferably has a bandwidth of maybe a few Hz, butDC power supply current (I_(PS)) can be calculated at any sample rateabove maybe 10 times the slow loop bandwidth. I_(PS) can be updated onceper half AC main cycle, or 60 Hz, but update can occur at possibly 10times per half-cycle or once every two half-cycles.

The I_(AVE) is, in essence, used to generate a series of GATE pulsesapplied to a flyback converter 68 via an I_(SNS) controlled through theprimary winding 70 of flyback circuit 68, all of which are more fullydescribed in FIG. 11 . The I_(AVE) signal is used to implement andregulate flyback converter 68 through transitions of the GATE pulses,wherein the GATE pulses are derived through a combination of T_(PON) andI_(PS) at the output of I_(AVE) map circuit 74. Details of circuit 74 asa sequential state machine are more fully described in FIG. 8 . Circuit74 produces I_(PS) and T_(PON) depending on the magnitude of I_(AVE).Details of the mapping function needed to generate I_(PS) and T_(PON)are described in relation to FIG. 8 . T_(PON) is used by a slow timercircuit to generate a power supply enable signal (P_(SEN)) having aduration of the T_(PON) duration up to maximum time of the power supplybeing on (MAX T_(PON)), whose value is used by circuit 74.

The value of when the DC power supply is on for a maximum duration (MAXT_(PON)), more fully described in FIG. 8 , is derived when controlcircuit 48 detects the L_(SNS) value for determining the conductionangle and subtracting a predetermined offset parameter. The P_(SEN)signal is used to trigger the fast timer circuit; specifically, toproduce certain signals, such as T_(PER) and T_(G2I) used by I_(ACT)calculation circuit 86 to produce the actual instantaneous current drawnfrom the AC main and applied to comparator 88 that determines the errorbetween I_(PS) and I_(ACT). That error from comparator 88 is filtered todetermine the duration at which each pulse of the GATE signal is in anactive logic state, e.g., logic value high shown as T_(GATE). T_(GATE)is used by fast timer circuit 82 to generate the signals necessary byI_(ACT) calculation circuit 86 to readjust I_(ACT) so that the actualinstantaneous draw resolves back to the DC power supply current (I_(PS))applied at each conduction angle per one half AC mains cycle to the LEDload. Further details of the operation of fast control loop 58 are morefully described in the timing diagram of FIG. 12 . The drive currentapplied to the LED load is therefore substantially proportional to theDC power supply current (I_(PS)) averaged over multiple cycles of the ACmain (I_(AVE)), taking into account other current needed to operate allthe other circuits DC circuits associated with the illumination device.For example, when the power supply is on for a maximum duration, thedrive current is substantially proportional to the DC power supplycurrent. However, when the power supply is on for less than the maximumduration, the drive current is substantially proportional to the DCpower supply current minus a predetermined amount of current needed tooperate the DC circuits. For example, the LED load can consume, forexample, 17 W while the remaining DC circuits can consume, for example,0.5 W.

Circuit 74 determines both the power supply current (I_(PS)) and thelength of time (T_(PON)) per ½ AC mains cycle in which voltage isapplied to the output capacitor coupled to V_(DC) which, in turn,supplies power to the second stage which then applies power (i.e., drivecurrent) to the LED load. PLL 52 and logic within control block 48 (FIG.15 ) determine the maximum amount of time that the first stage 38 ofpower supply 36 is on and can run during each ½ cycle of the AC mains(MAX T_(PON)).

Referring to FIGS. 7 and 8 , circuit 74 is a sequential machine thatcompares the incoming I_(AVE) against certain values, as shown bydecision block 90. Block 90 determines if I_(AVE)≤a predeterminedminimum value (e.g., 100 mA)×120 Hz×MAX T_(PON). If the answer to block90 is yes, then:I _(PS)=a predetermined minimum value (e.g., 100 mA); andT _(PON)=(I _(AVE)/a predetermined minimum value)×( 1/120 Hz).If the answer to block 90 is no, then:I _(PS) =I _(AVE)×(1/MAX T _(PON)×120 Hz); andT _(PON)=MAX T _(PON).

The above equations simply note that when determining the magnitude ofthe power supply current (I_(PS)) and the actual time that the powersupply operates (T_(PON)), a comparison is needed of I_(AVE) againstcertain parameters. The equations indicate that as I_(AVE) increases,I_(PS) remains at a predetermined minimum value, e.g., 100 mA, andT_(PON) increases. When I_(PS) and T_(PON) increases and onceT_(PON)=MAX T_(PON), I_(PS) increases from the predetermined minimumvalue, e.g., 100 mA. Block 90 merely indicates that a minimum powersupply current is maintained and does not increase until after the timethat the power supply operates (T_(PON)) and is equal to the maximumtime in which the power supply can operation (MAX T_(PON)). In thisfashion, the power supply current is always maintained above apredetermined minimum value and the duration in which the power supplyis on will never exceed MAX T_(PON) derived as an offset from theconduction angle as computed by the control circuit. The minimum valueis set to be greater than the hold current needed to keep the triac inthe conducting state and prevent such from resetting.

Once the power supply current (I_(PS)) and the actual time in which thepower supply operates (T_(PON)) is determined, the actual instantaneouscurrent through first stage 38 (I_(ACT)) is controlled by fast controlloop 58. Fast control loop 58 has a much higher bandwidth than slowcontrol loop 60. For example, fast control loop 58 may be in excess of 1kHz, while slow control loop 60 may have a bandwidth of only a few Hz.

Fast control loop 58 is used to compare the actual instantaneous currentthrough the AC/DC converter (I_(ACT)) to the power supply current(I_(PS)). The power supply current is that which exists through secondstage 40 of power supply 36. The difference between the power supplycurrent and the actual instantaneous AC/DC current is compared bycomparator 88, and difference is low-pass filtered by filter 89, whichis an integrator, to produce the time that the gate is at a logic activestate or logic high (T_(GATE)). The difference between the instantaneouscurrent (I_(ACT)) and the power supply current (I_(PS)) is basically thedifference between each instantaneous moment in time versus the currentover the entire ½ cycle of the AC mains or the current of the AC mains.The actual instantaneous current (I_(ACT)) is sampled at the fast timerrate of at least 50 kHz, which is the switching rate of signal GATE. Thepower supply current (I_(PS)) is sampled at a much lower rate, e.g.,less than ½ the AC mains cycle. Fast control loop 58 operates to holdthe actual instantaneous current (I_(ACT)) to the power supply current(I_(PS)) over time.

Accordingly, slow control loop 60 controls V_(DC) and fast control loop58 controls the actual instantaneous current (I_(ACT)) drawn from the ACmains. For relatively low average currents (I_(AVE)), fast control loop58 holds I_(ACT) to a predetermined minimum value, e.g., 100 mA, and theamount of time (T_(PON)) that the power supply 36 operates; T_(PON) canvary, yet the I_(AVE) is maintained to no less than the predeterminedminimum value, e.g., 100 mA. As noted, once T_(PON) reaches MAX T_(PON)determined by control circuit 48, then I_(PS) increases based on anyneeded increase effectuated by software within the controller or throughdirect user interaction via radio 54 or a wired link.

As noted in FIG. 7 , the I_(ACT) calculation block 86 uses the gatetiming (T_(GATE)) and the current sense comparator output (I_(CMP)) todetermine I_(ACT). How that determination takes place is described inmore detail with reference to FIGS. 9, 10, and 12 . Turning to FIG. 11 ,AC/DC analog circuit 62 (FIG. 7 ) is shown in circuit form. AC/DC analogcircuit 62 comprises damper circuit 100, bleeder circuit 102, andflyback circuit 68. AC/DC analog circuit 62 also includes control powersupply 104 and circuitry needed to produce the line sense (L_(SNS)) fromV_(IN) and a feedback voltage (V_(FB) or V_(IN)) multiplexed from ashared analog-to-digital converter (ADC) 106, that either inputs adivided-down V_(DC) through resistor dividers or the V_(IN) fromdifferential amplifier 46 (FIG. 6 ). The V_(IN) voltage output from ADC106 is at a lower voltage than the AC mains but is proportional to theAC mains and is purposely used to detect the conduction angle outputfrom the dimmer. V_(SUPPLY) provides voltage needed for the digitalcircuits, including the control circuit.

Damper circuit 100 is simply a transistor placed in parallel with aresistor. The resistor is one having a fairly small value such as, forexample, 150 ohms. The resistor damps input transients when the /DMPsignal output from slow timer circuit 18 transitions to an active lowstate. The purpose of damping circuit 100 is to ensure that dimmercircuit 30 operates properly. For example, when a triac is used for thedimmer and the triac transitions on, a large voltage is applied to thepower supply. That voltage appears at the leading edge of, for example,the conduction angle (FIGS. 3, 4 ). That large voltage oscillates as afairly large transient current. To minimize the oscillation and toprevent the triac from resetting, the AC/DC analog 62 includes dampingcircuit 100 to place a low impedance resistor onto the capacitive loadof the rectified and filtered AC main line to damp the oscillations.Slow timer 80 sets the damp signal (/DMP) active during the transientsto connect the passive load of the relatively small resistor by turningthe parallel-coupled transistor off. The /DMP signal is maintained at anactive low between each of a pair of conduction angles, all set by slowtimer 80. The active damp extends past the leading edge of theconduction angle to remove or damp the oscillations, and shortlythereafter is deactivated by transitioning on the parallel-coupledtransistor so that the power supply begins operating with a largeinitial T_(GATE) time of T_(INT). The initially large T_(GATE) thatconsists of T_(INT) is shown in FIG. 12 . T_(INT) is predetermined toproduce an active input impedance roughly equal to the passive inputimpedance produced when /DMP is active. A larger T_(INT) versussubsequent T_(GATE) causes the GATE voltage to extend for a longerduration during initial power supply activity so input impedance uponthe line voltage V_(HV) (V_(HV)/I_(ACT)) is roughly equal to the passiveimpedance of the resistor within damping circuit 100 when /DMP isactive. Referring to FIG. 12 , T_(INT) only exists for the firstT_(GATE) duration and, thereafter, subsumes back to the normal T_(GATE)duration.

As noted, certain leading edge or trailing edge triac dimmers requirecurrent to be drawn through the AC main line throughout each cycle inorder for the conduction angle to be measured properly. After firing, atriac will typically turn off once the current through that triac dropsbelow a certain level. For example, the minimum I_(PS), e.g., 100 mA, issufficient to hold the triac on. However, a triac may reset after powersupply 36 turns off, but before the line voltage V_(HV) drops to near 0.If the triac of dimmer 30 resets prior to the line voltage V_(HV)dropping to near 0, controller 48 may measure incorrect dimmer angles,i.e., instead of producing the correct dimmer angle or conduction angleand, thus, the correct MAX T_(PON), the measured conduction angle andresulting MAX T_(PON) may be incorrect. Therefore, slow timer 80produces a bleed signal (BLEED) to instruct circuit 102 to draw a fixedcurrent of a predetermined minimum value, e.g., 100 mA, during timeswhen the power supply 36 is not active and the conduction angle is beingmeasured. Absent an accurate conduction angle measurement, MAX T_(PON)cannot be output from controller 48, which will dictate when the DCpower supply current will be at 100 mA and will exceed, for example, 100mA when the time the power supply is on reaches the measured MAXT_(PON).

Similar to holding on a triac of dimmer 30, the LED load must draw thedrive current I_(AVE) and the power supply current I_(PS) from thetrailing edge dimmer when measuring the conduction angle. A trailingedge dimmer turns on when the line voltage is near 0 and can turn offwhen the line voltage is high or at its peak. The line input capacitancemust be discharged rapidly when the trailing edge dimmer turns off inorder for controller 48 to determine the conduction angle. During cyclesin which controller 48 measures the conduction angle, the BLEED signalgoes active after the power supply turns off after T_(PON) ends or whenT_(PON)=MAX T_(PON) turns off. The falling edge of L_(SNS) indicates thepoint at which the conduction angle turns off, which puts the powersupply in what is known as a current pulse mode (CPM) and turns on thedamper circuit with /DMP active low while the dimmer circuit is notconducting. However, the periodic pulses of the GATE signal thatoccurred during the conduction cycle are maintained in an active logicvalue, such as logic voltage high during CPM, shown in FIG. 13 .

Turning to FIG. 11 , control circuit 104 of power supply 62 comprisesthe start-up circuit 110 coupled to a V_(SUPPLY) bypass capacitor 112and auxiliary winding 114. When power is first applied to the LED lamp,V_(HV) goes above the Zener voltage of the Zener diode within circuit110. V_(SUPPLY) bypass capacitor 112 charges up to the Zener voltageminus the transistor gate source voltage, and minus the diode drop ofcircuit 110. When flyback converter 68 is operating, auxiliary winding114 continually charges capacitor 112 through diode 120 to a slightlyhigher voltage than circuit 110 applied to capacitor 112, which thenturns off circuit 110. Accordingly, circuit 110 is simply used to chargeup to and past the Zener voltage via auxiliary winding 114. Once thecharge up has occurred, circuit 110 is deactivated and, thereafter, doesnot burn power from the AC mains through DC power supply 62.

Flyback converter 68 comprises a transformer with primary winding 70 andsecondary winding 124. When the GATE signal is high, primary winding 70conducts and current through increases linearly with time. The currentsense resistor R_(SNS) and comparator 126 produces a current comparatoroutput I_(CMP). I_(CMP) indicates when the primary current reaches acertain value set by the I_(DAC), where I_(DAC) arrives from a parameterset within the control circuit processor. Fast timer 82 (FIG. 7 ) usesImp to determine when to turn GATE off. When GATE goes low, the primarycurrent drops to 0 and the energy stored in the transformer coreproduces current in secondary winding 124. The secondary winding currentflows through the diode and into the V_(DC) bypass capacitor 130 and tothe LED load 42 (FIG. 6 ). A small portion of the energy stored in thecore produces current in the auxiliary winding 114 that passes throughthe diode and into capacitor 112. Once all the energy stored in the coreis depleted, the current in both secondary winding 124 and auxiliarywinding 114 stops flowing and the voltage across both windingscollapses. Zero-crossing detect (ZCD) comparator 134 and itscorresponding DAC detect this collapse and sets ZCD to a logic highvalue. Shown in FIG. 12 , fast timer 82 uses this rising edge of ZCD toset GATE high, starting another power supply computation cycle.

Turning now to FIGS. 7 and 12 in combination, FIG. 12 illustrates thetiming of the signals in and out of fast timer 82 of FIG. 7 . Powersupply enable (P_(SEN)) signal, GATE, I_(CMP), and ZCD are logic levelsignals, while T_(GATE), T_(PER), T_(G2I), and I_(TNT) are numbers. Slowtimer 80 activates the P_(SEN) signal by first detecting L_(SNS).L_(SNS) is output from the comparator whose input is set by the L_(DAC)parameter of the control circuit and V_(IN). L_(SNS) determines when therectified AC main is above or below a certain relatively low voltage,e.g., 20 volts. Slow timer 80 and controller 48 use the rising edge ofL_(SNS) to initiate the power supply start sequence and the conductionangle measurements, respectively. Referring to FIG. 13 , it is fromL_(SNS) that P_(SEN) is derived from slower timer 80 in response toL_(SNS) going high and deactivating P_(SEN) after the time specified byT_(PON). As shown in FIG. 12 , first stage 38 of power supply 36 isactive when P_(SEN) is high, as shown by T_(PON). The AC/DC converterstarts switching with a relatively long GATE high time T_(GATE) ofT_(INT), which produces an active load roughly equal to the damperpassive load. The high bandwidth current control loop or fast controlloop 58 then gradually adjusts T_(GATE) and consequently I_(ACT) untilI_(ACT) equals the current I_(PS), set by the low bandwidth or slowcontrol loop 60. This reduction T_(GATE) is illustrated in the GATEsignal and the sequence of GATE pulses of FIG. 12 .

While the time GATE is high is specified by T_(GATE), the time that GATEis low is determined by ZCD. ZCD goes high when all the energy in thetransformer core of flyback converter 68 has been transferred andsecondary winding 124 and auxiliary winding 114 current drops to 0. Assuch, a rising edge of ZCD will trigger the start of another AC/DCcomputation cycle with GATE again going high. Accordingly, the risingedge of ZCD turns GATE on.

When GATE goes high, the current flowing through primary winding 70increases linearly with time. When the primary winding current reaches acertain value determined by IDAC and R_(SNS), I_(CMP) goes high. Thetime from GATE going high to I_(CMP) going high is shown as T_(G2I) inFIG. 12 ; the period of GATE is shown as T_(PER). The I_(ACT)calculation block 86 (FIG. 7 ) uses T_(G2I) and T_(PER), along withT_(GATE), to determine the actual instantaneous current I_(ACT) drawnfrom the AC main line. Accordingly, while the rising edge of ZCD turnsGATE on, the expiration of time T_(GATE) from the fast loop integratorthat turns GATE off. It is duration T_(GATE) and the series of pulsesfor T_(GATE) that determine I_(PS) and the drive current that flows intothe LED load.

Turning now to FIG. 13 , illustrated is a timing diagram of the signalsin and out of slow timer 80 (FIG. 7 ) in relation to V_(HV), GATE, andthe PLL ZCD signal from controller 48. In the example shown, dimmer 30is adjusted to produce roughly 90° of conduction angle. The rectifiedV_(HV) to first stage 38 of power supply 36 comprises rectified ¼-cyclesine waves. With L_(DAC) sent from the control block configured toswitch L_(SNS) when V_(HV) is about 15 volts, L_(SNS) goes high whenthis leading-edge dimmer turns on and then goes low very close to theend of each ¼-cycle. Damper circuit 100 turns on with /DMP going low,with L_(SNS) going low which turns off a fixed delay after L_(SNS) goeshigh. That fixed delay is necessary to remove the transients fromV_(HV). Moreover, the fixed delay is predetermined to be sufficient forall major transients to subside. Shown in FIG. 11 , while /DMP is low,the resistor placed in series with the lamp power input capacitance, iscoupled to V_(HV).

Referring to FIGS. 13-14 , two sets of GATE, P_(SEN), BLEED, and I_(HV)are shown. The input current is the current drawn from the AC mains;specifically, from V_(HV). The (A) group illustrates the timing when theAC/DC stage of the power supply is drawing a relatively large amount ofpower from the AC mains, wherein the power duration of T_(PON)=MAXT_(PON). The (B) group illustrates the timing when the AC/DC stage ofthe power supply is drawing a relatively little power, where T_(PON)<MAXT_(PON) and I_(PS)=predetermined minimum value, e.g., 100 mA. In boththe (A) and (B) groups illustrated in FIGS. 13-14 , the AC/DC converterfirst stage turns on when the damper circuit turns off with /DMP goinghigh. P_(SEN) goes high and GATE starts switching during T_(PON) (FIG.14 ) and during MAX T_(PON) (FIG. 13 ). For example, P_(SEN) (A) goeslow and GATE (A) stops switching after the time specified by MAXT_(PON). The AC/DC converter can efficiently draw power from the AC mainline only when V_(HV) is above a certain voltage. MAX T_(PON) ispredetermined to ensure that V_(HV) is sufficiently high whenever theAC/DC converter is on.

While L_(SNS) is low, the first stage AC/DC converter operates in thecurrent pulse mode (CPM). CPM provides a DC load for the dimmer and inCPM, the GATE commutes solely on I_(CMP) and ZCD. GATE goes high withZCD and low with I_(CMP). FIGS. 13-14 illustrate GATE (A) and (B)remaining high when L_(SNS) is low since typically that is the case whenV_(HV) is nominally 0. However, CPM enables the LED load to dischargestray capacitances and sink any dimmer leakage currents or otherparasitics.

BLEED (A) and (B) are active between P_(SEN) going low and L_(SNS) goinghigh. When BLEED is high, a predetermined fixed current, e.g., 100 mA,is drawn from the AC main line keeping the triac conducting and enablesthe conduction angle to be accurately measured. BLEED is active whenL_(SNS) is low and the dimmer is not conducting for the same reason thatthe AC/DC converter first stage operates in CPM. The bleeder helpsdischarge any parasitics. Preferably, the bleeder need not be activebetween every pair of conduction angles and, possibly, need only beactive between every eighth or twentieth pair of conduction angles,since the bleeder does draw significant current and may not be necessaryto bleed after every conduction angle. Preferably, the conduction angleneed only be measured at every half AC mains cycle, and when theconduction angle is measured, bleeder is active.

The I_(HV) (A) and (B) curves illustrate the current drawn from the ACmain line through V_(HV) for the relatively high and low currentconditions shown. In both cases, I_(HV) quickly ramps to the same highlevel when the triac dimmer initially turns on. This current isdetermined by the damping resistor within the damping circuit, and isgenerally fairly small, e.g., 150 ohms. When the P_(SEN) goes high, theAC/DC first stage draws roughly this same high current actively. TheI_(HV) current then decreases to I_(PS) determined by the low bandwidthor slow control loop 60 over a period of time. In the (A) example,I_(PS) is larger than 100 mA since T_(PON)=MAX T_(PON); I_(HV) drops to100 mA drawn by the bleeder after P_(SEN) goes low and BLEED (A) goeshigh. In the (B) example, I_(PS) is equal to 100 mA since T_(PON)<MAXT_(PON); I_(HV) simply stays at 100 mA since both the bleeder and theAC/DC converter first stage are set to draw 100 mA. Of course, thepredetermined minimum value can be set at any value, with 100 mA beingone example. As noted, BLEED does not need to be active every cycle, butonly during angle measurement cycles, possibly between every eighth,twentieth, or more pairs of conduction angles.

Turning now to FIGS. 9-10 , the I_(ACT) calculation 86 (FIG. 7 ) logicis shown. Specifically, a state diagram logic block and a timing diagramof I_(ACT) computation point taken from I_(PK) value, as well asT_(GATE) and T_(G2I) timing values. First, the I_(ACT) calculation mustdetermine a peak primary current (I_(PK)) through the primary winding70.I _(PK)=(T _(GATE) /T _(G2I))×I _(SNS)I _(ACT)=(I _(PK)/2)×(T _(GATE) /T _(PER))Knowing the peak current through the primary winding, I_(ACT) can be setnear a midpoint and derived therefrom based on readings of T_(GATE), andT_(PER). Thus, from the peak primary current, the actual primary currentcan be derived, with I_(ACT) set to I_(PS) within fast control loop 58(FIG. 7 ). I_(SNS) is shown to be the current through R_(SNS) (FIG. 11). The average current through primary winding I_(ACT) over one AC/DCcomputation cycle is ½ the peak current I_(PK) scaled by the time GATEis high, T_(GATE)/one computation cycle T_(PER).

Referring to FIG. 15 , control circuit 48 is shown; specifically, theAC/DC converter first stage functionality, comprising PLL 52 andmicroprocessor 50. Microprocessor 50 configures the parameters in theAC/DC first stage and DC/DC second stage converters of power supply 36,and also interfaces to radio 54 to communicate control and statusmessages. V_(IN) being a scaled version of the line input voltage isdigitized and forwarded to PLL 52. PLL 52 qualifies such samples withL_(SNS) and uses successive samples to determine the phase error betweenthe PLL output and the AC main line cycle. The phase error is filteredand then used to produce a digital sine wave in sync with the AC mainline voltage. The output of PLL 52 is a number from 1-360 representingthe AC mains phase as function of time. The PLL ZCD pulse is high whenthe phase equals 180° or 360°, indicating a zero-crossing detection ofthe conduction angle phase.

The L_(SNS) and PLL ZCD are forwarded to a set/reset latch 94 whoseoutput enables a counter 96 and low pass filter 98. The count value isused to compute the conduction angle from the dimmer regardless of howthat dimmer is set. An offset from processor 50 is compared with theconduction angle via comparator 100 to produce a maximum time in whichthe power supply is on (MAX T_(PON)). MAX T_(PON) and the conductionangle are used by slow control loop 60; specifically, I_(AVE) map 74(FIG. 7 ). Although the conduction angle and MAX T_(PON) are computed,it is not the conduction angle or MAX T_(PON) that determines the drivecurrent supplied to the LED load. Thus, the drive current, I_(PS), andI_(AVE) can be independent from the conduction angle output from thedimmer. Radio 54 illustrates one way in which to input control andstatus messages into processor 50. However, processor 50 can generatethe parameters shown to set comparator values (within, for example, theanalog portion of the power supply) based on software derived commandswithin processor 50 using various fetch routines from associated memorywithin processor 50. Processor 50 merely executes those commands toapply the appropriate parameters at the appropriate times onto, forexample, the analog portion of the power supply as well as upon the slowand fast control loops.

It will be appreciated that the various parameters and certainmagnitudes described herein are given by way of example only. Theparameters and magnitudes can be modified to any value for controllingthe LED load (both brightness and/or color) independent of the dimmerangle setting, and over a range also independent of a range of thedimmer angle setting. The DC power supply can accommodate and scale todimmers of differing conduction angle ranges, and those of relativelysmall maximum conduction angles such as, for example, 90°. By decouplingthe LED loads from the dimmer angle, the DC power supply can utilize thefull dimming range of 0-100% of the LED brightness by significantlyreducing and eliminating the dead travel that may be experienced at thetop and bottom of the dimming curve, where conventional dimmer settingsproduce no visible changes in LED light output. In fact, as long asthere is sufficient power to be pulled from the AC mains, the presentpower supply can adjust the lamp brightness downward to, for example,0.1% of the maximum lamp brightness. This minimum dimming achieved usingthe present power supply cannot be attained in conventional dimmer andAC/DC converter architecture. It will be readily appreciated thatdifferent parameters and values can be employed provided the aboveoutcomes are achieved without departing from the inventive concepts aswill be apparent to those skilled in art in view of this description. Itis intended that the following claims be interpreted to embrace all suchmodifications. The specification and drawings are to be regarded in anillustrative, rather than a restrictive, sense.

What is claimed is:
 1. An illumination device configured to receivepower from an alternating-current (AC) mains supply through a dimmer,the illumination device comprising: a light-emitting load configured toemit light; a power supply configured to conduct a supply current fromthe AC mains supply and produce a drive current through thelight-emitting load when the power supply is active; and a controlcircuit coupled to receive a phase-cut signal from the dimmer, thecontrol circuit configured to control the power supply to be active fora length of an operating time period during a conduction period of ahalf-cycle of the phase-cut signal, the control circuit configured todetermine a maximum duration of the operating time period during thehalf-cycle based on a length of the conduction period of the phase-cutsignal; wherein the power supply comprises a first stage configured toproduce a direct-current (DC) voltage from the phase-cut signal, and asecond stage configured to receive the DC voltage and produce the drivecurrent through the light-emitting load; wherein the control circuit isconfigured to receive a feedback voltage indicating a magnitude of theDC voltage and to determine the average magnitude of the supply currentto be drawn from the AC mains supply in response to the feedbackvoltage; and wherein the control circuit is configured to set the lengthof the operating time period equal to the maximum duration when anaverage magnitude of the supply current to be drawn from the AC mainssupply over multiple cycles is greater than a threshold, and set thelength of the operating time period to be less than the maximum durationwhen the average magnitude of the supply current to be drawn from the ACmains supply is less than the threshold.
 2. The illumination device ofclaim 1, wherein the control circuit is configured to determine adirect-current (DC) magnitude of the supply current to be drawn from theAC mains supply during the conduction period of the half-cycle inresponse to the maximum duration of the operating time period and theaverage magnitude of the supply current to be drawn from the AC mainssupply.
 3. The illumination device of claim 2, wherein, when the averagemagnitude of the supply current to be drawn from the AC mains supply isless than the threshold, the control circuit is configured to set the DCmagnitude of the supply current to be drawn from the AC mains supplyduring the conduction period of the half-cycle to a predeterminedminimum value.
 4. The illumination device of claim 3, wherein, when theaverage magnitude of the supply current to be drawn from the AC mainssupply is less than the threshold, the control circuit is configured toset the length of the operating time period of the power supply as afunction of the average magnitude of the supply current to be drawn fromthe AC mains supply and the predetermined minimum value of the supplycurrent.
 5. The illumination device of claim 3, wherein the controlcircuit is configured to determine a value of the threshold as afunction of the maximum duration of the operating time period and thepredetermined minimum value of the supply current.
 6. The illuminationdevice of claim 2, wherein, when the average magnitude of the supplycurrent to be drawn from the AC mains supply is greater than thethreshold, the control circuit is configured to set the DC magnitude ofthe supply current to be drawn from the AC mains supply during theconduction period of the half-cycle as a function of the maximumduration of the operating time period and the average magnitude of thesupply current to be drawn from the AC mains supply.
 7. The illuminationdevice of claim 1, wherein the control circuit is configured to measurea conduction angle of the phase-cut signal and determine the length ofthe conduction period of the phase-cut signal based on the measuredconduction angle.
 8. The illumination device of claim 7, wherein thecontrol circuit is configured to set the maximum duration of theoperating time period equal to the length of the conduction period ofthe phase-cut signal minus a predetermined offset parameter.
 9. Theillumination device of claim 1, wherein, when the average magnitude ofthe supply current to be drawn from the AC mains supply is less than thethreshold, the control circuit is configured to set the length of theoperating time period of the power supply as a function of the averagemagnitude of the supply current to be drawn from the AC mains supply.10. The illumination device of claim 1, wherein the control circuit isconfigured to determine a value of the threshold based on the maximumduration of the operating time period.
 11. The illumination device ofclaim 1, further comprising: a radio configured to communicate messages;wherein the control circuit is configured to set a magnitude of thedrive current in response to the messages received via the radio. 12.The illumination device of claim 1, wherein the average magnitude of thesupply current over multiple cycles of the AC mains supply isproportional to a magnitude of the drive current conducted through thelight-emitting load.
 13. A method of controlling a light-emitting loadof an illumination device that receives power from analternating-current (AC) mains supply through a dimmer, the methodcomprising: receiving a phase-cut signal from the dimmer; measuring aconduction angle of the phase-cut signal; controlling the light-emittingload to emit light by causing a power supply to conduct a supply currentfrom the AC mains supply and produce a drive current through thelight-emitting load when the power supply is active; controlling thepower supply to be active for a length of an operating time periodduring a conduction period of a half-cycle of the phase-cut signal;determining the length of the conduction period of the phase-cut signalbased on the measured conduction angle; determining a maximum durationof the operating time period during the half-cycle based on a length ofthe conduction period of the phase-cut signal; setting the length of theoperating time period of the power supply to the maximum duration whenan average magnitude of the supply current to be drawn from the AC mainssupply over multiple cycles is greater than a threshold; setting themaximum duration of the operating time period equal to the length of theconduction period of the phase-cut signal minus a predetermined offsetparameter; and setting the length of the operating time period of thepower supply to be less than the maximum duration when the averagemagnitude of the supply current to be drawn from the AC mains supply isless the threshold.
 14. The method of claim 13, further comprising:determining a direct-current (DC) magnitude of the supply current to bedrawn from the AC mains supply during the conduction period of thehalf-cycle in response to the maximum duration of the operating timeperiod and the average magnitude of the supply current to be drawn fromthe AC mains supply.
 15. The method of claim 14, further comprising:when the average magnitude of the supply current to be drawn from the ACmains supply is less than the threshold, setting the DC magnitude of thesupply current to be drawn from the AC mains supply during theconduction period of the half-cycle to a predetermined minimum value ofthe supply current.
 16. The method of claim 15, further comprising: whenthe average magnitude of the supply current to be drawn from the ACmains supply is less than the threshold, setting the length of theoperating time period of the power supply as a function of the averagemagnitude and the predetermined minimum value of the supply current. 17.The method of claim 15, further comprising: determining a value of thethreshold as a function of the maximum duration of the operating timeperiod and the predetermined minimum value of the supply current. 18.The method of claim 14, further comprising: when the average magnitudeof the supply current to be drawn from the AC mains supply is greaterthan the threshold, setting the DC magnitude of the supply current to bedrawn from the AC mains supply during the conduction period of thehalf-cycle as a function of the maximum duration of the operating timeperiod and the average magnitude of the supply current to be drawn fromthe AC mains supply.
 19. The method of claim 18, further comprising:determining a value of the threshold based on the maximum duration ofthe operating time period.
 20. The method of claim 13, furthercomprising: when the average magnitude of the supply current to be drawnfrom the AC mains supply is less than the threshold, setting the lengthof the operating time period of the power supply as a function of theaverage magnitude of the supply current to be drawn from the AC mainssupply.